HUGO CAVALCANTE saw the disaster coming. From his lab at the Federal University of Paraíba in Brazil, he detected the warning signs of an epic crash. At the last minute, he managed to nudge his system back to safety. Crisis averted.

OK, so Cavalcante's impending crisis was only a pair of credit-card-sized circuits that were about to start oscillating out of sync – hardly the stuff of the evening news. But the experiment is the first to show that a class of extreme events, colourfully called dragon-kings, can be predicted and suppressed in a real, physical system. The feat suggests that some day we may also be able to predict, or in some cases prevent, some of the catastrophes in the real world that seem unstoppable, including financial crashes, brain seizures and storms.

"People were hoping if you could forecast extreme events, maybe we could find a way to control them," says Cavalcante's colleague Daniel Gauthier at Duke University in Durham, North Carolina. "We were able to completely suppress the dragon-king events."

Dragon-kings aren't the first animal used to describe a class of catastrophic events. In 2001, Nassim Taleb published a book called The Black Swan, his name for catastrophes that always catch us off-guard. But though difficult to predict, black swans actually fall within an accepted mathematical distribution known as a power law, which says there will be exponentially more small events than large ones (see diagram).

Now there's another beast to reckon with. In 2009, Didier Sornette at the Swiss Federal Institute of Technology in Zurich reported that some events lift their heads above the power law's parapet, the way a king's power and wealth vastly outstrip that of the more plentiful peasant. So big that they should be rare, these events have a greater probability of occurring than a power law would mandate.

"There seem to be certain extremes that happen much more often than they should if you just believe the power-law distribution predicted by their smaller siblings," Sornette says.

He christened them dragon-kings. The dragon part of the name stems from the fact that these events seem to obey different mathematical laws, just as a dragon's behaviour differs from that of the other animals.

Sornette got his first whiff of dragon-kings when studying cracks that develop in spacecraft. Since then, he has spotted them everywhere, from a rainstorm that hit Venezuela in 1999 and the financial crashes in 2000 and 2007, to some epileptic seizures.

But he wasn't satisfied with merely recognising dragon-kings. The fact that they don't follow a power law suggests they are being produced by a different mechanism, which raises the possibility that, unlike events that follow the power law, dragon-kings may be predictable.

Enter Cavalcante and Gauthier's oscillating circuits. Gauthier spent the early 1990s studying pairs of identical circuits that behaved chaotically on their own, but would synchronise for long periods of time when coupled in a certain way. "It's a little bit politically incorrect, but it's sometimes called the 'master-slave' configuration," Gauthier says. He coupled the two circuits by measuring the difference between the voltages running through them, and injecting a current into the "slave" circuit to make it more like the "master". Most of the time this worked and the two would oscillate together like a pair of swinging pendulums, with only slight deviations away from synchronisation.

But every so often, the slave would stop following the master and march to its own beat for a short time, before getting back in step. Gauthier realised at the time that there were recognisable signs that this disconnect was about to happen. It wasn't until he saw Sornette's work that he checked for dragon-kings.

He and his colleagues have now shown that the differences in the circuits' voltages during these desynchronisations are indeed dragon-kings. "They were as big as the system would physically allow, like a major disaster," Gauthier says.

The pair went on to show that they could reliably forecast when a big event was about to happen: whenever the differences between the circuits' oscillations decreased to a certain value, a leap of dragon-king proportions was almost always imminent. And once they saw it coming, they found they could apply a small electrical nudge to the slave circuit to make sure it didn't tear away from its master (Physical Review Letters, doi.org/p44).

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